DeFi legos and protocol composability on Ethereum and L2s. Major protocols per chain — Aerodrome on Base, GMX/Pendle on Arbitrum, Velodrome on Optimism — plus mainnet primitives (Uniswap, Aave, Compound, Curve). How they work, how to build on them, and how to combine them. Use when building DeFi integrations, choosing protocols on a specific L2, designing yield strategies, or composing existing protocols into something new.
DeFi TVL: Check DeFi Llama for current Ethereum DeFi TVL. If you're quoting numbers from 2023-2024, they're stale.
Uniswap V4 is live. Launched mainnet January 31, 2025 on 10+ chains. V4 introduced a hooks system — custom logic attached to pools (dynamic fees, TWAMM, limit orders, custom oracles). This is the biggest composability upgrade since flash loans. PoolManager addresses are different per chain (NOT deterministic like V3).
Costs changed everything: A flash loan arbitrage on mainnet costs ~$0.05-0.50 in gas now (was $5-50). This opens composability patterns that were previously uneconomical.
The dominant DEX on each L2 is NOT Uniswap. Aerodrome and Velodrome merged into Aero (November 2025, Dromos Labs) — the unified DEX dominates both Base and Optimism. Camelot is a major native DEX on Arbitrum. Don't default to Uniswap on every chain.
| Protocol | Contract | Mainnet Address |
|---|---|---|
| Uniswap V2 Router | Router | 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D |
| Uniswap V2 Factory | Factory | 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f |
| Uniswap V3 Factory | Factory | 0x1F98431c8aD98523631AE4a59f267346ea31F984 |
| Uniswap V3 SwapRouter02 | Router | 0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45 |
| Uniswap V4 PoolManager | PoolManager | 0x000000000004444c5dc75cB358380D2e3dE08A90 |
| Uniswap Universal Router (V4) | Router | 0x66a9893cc07d91d95644aedd05d03f95e1dba8af |
| Aave V3 Pool | Pool | 0x87870Bca3F3fD6335C3F4ce8392D69350B4fA4E2 |
See addresses/SKILL.md for complete multi-chain address list including L2-native protocols (Aerodrome, GMX, Pendle, Velodrome, Camelot, SyncSwap, Morpho).
Hooks let you add custom logic that runs before/after swaps, liquidity changes, and donations. This is the biggest composability upgrade since flash loans.
import {BaseHook} from "v4-periphery/src/utils/BaseHook.sol";
import {IPoolManager} from "v4-core/interfaces/IPoolManager.sol";
import {PoolKey} from "v4-core/types/PoolKey.sol";
import {BeforeSwapDelta, BeforeSwapDeltaLibrary} from "v4-core/types/BeforeSwapDelta.sol";
contract DynamicFeeHook is BaseHook {
constructor(IPoolManager _manager) BaseHook(_manager) {}
function getHookPermissions() public pure override returns (Hooks.Permissions memory) {
return Hooks.Permissions({
beforeInitialize: false,
afterInitialize: false,
beforeAddLiquidity: false,
afterAddLiquidity: false,
beforeRemoveLiquidity: false,
afterRemoveLiquidity: false,
beforeSwap: true, // ← We hook here
afterSwap: false,
beforeDonate: false,
afterDonate: false,
beforeSwapReturnDelta: false,
afterSwapReturnDelta: false,
afterAddLiquidityReturnDelta: false,
afterRemoveLiquidityReturnDelta: false
});
}
// Dynamic fee: higher fee during high-volume periods
function beforeSwap(
address,
PoolKey calldata key,
IPoolManager.SwapParams calldata params,
bytes calldata
) external override returns (bytes4, BeforeSwapDelta, uint24) {
// Return dynamic fee override (e.g., 0.05% normally, 0.30% during volatility)
uint24 fee = _isHighVolatility() ? 3000 : 500;
return (this.beforeSwap.selector, BeforeSwapDeltaLibrary.ZERO_DELTA, fee | 0x800000);
}
}
Hook use cases with real code patterns:
These patterns are now economically viable even for small amounts due to sub-dollar gas:
Borrow from Aave → swap on Uniswap for profit → repay Aave. All in one transaction. If unprofitable, reverts (lose only gas: ~$0.05-0.50).
Deposit ETH on Aave → borrow stablecoin → swap for more ETH → deposit again → repeat. Gas cost per loop: ~$0.02 on mainnet, negligible on L2.
Route swaps across multiple DEXs for best execution. 1inch and Paraswap check Uniswap, Curve, Sushi simultaneously.
Standard vault interface — the "ERC-20 of yield." Every vault exposes the same functions regardless of strategy.
import {ERC4626} from "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";
import {ERC20, IERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
contract SimpleYieldVault is ERC4626 {
constructor(IERC20 asset_)
ERC4626(asset_)
ERC20("Vault Shares", "vSHARE")
{}
// totalAssets() drives the share price
// As yield accrues, totalAssets grows → shares worth more
function totalAssets() public view override returns (uint256) {
return IERC20(asset()).balanceOf(address(this)) + _getAccruedYield();
}
}
// Usage: deposit/withdraw are standardized
// vault.deposit(1000e6, msg.sender); // deposit 1000 USDC, get shares
// vault.redeem(shares, msg.sender, msg.sender); // burn shares, get USDC back
// vault.convertToAssets(shares); // how much USDC are my shares worth?
Why ERC-4626 matters: Composability. Any protocol can integrate any vault without custom adapters. Yearn V3, Aave's wrapped tokens, Morpho vaults, Pendle yield tokens — all ERC-4626.
import {FlashLoanSimpleReceiverBase} from
"@aave/v3-core/contracts/flashloan-v3/base/FlashLoanSimpleReceiverBase.sol";
import {IPoolAddressesProvider} from
"@aave/v3-core/contracts/interfaces/IPoolAddressesProvider.sol";
contract FlashLoanArb is FlashLoanSimpleReceiverBase {
constructor(IPoolAddressesProvider provider)
FlashLoanSimpleReceiverBase(provider) {}
function executeArb(address token, uint256 amount) external {
// Borrow `amount` of `token` — must repay + 0.05% fee in same tx
POOL.flashLoanSimple(address(this), token, amount, "", 0);
}
function executeOperation(
address asset,
uint256 amount,
uint256 premium, // 0.05% fee
address,
bytes calldata
) external override returns (bool) {
// --- Your arbitrage logic here ---
// Buy cheap on DEX A, sell expensive on DEX B
// Must end with at least `amount + premium` of `asset`
uint256 owed = amount + premium;
IERC20(asset).approve(address(POOL), owed);
return true; // If unprofitable, revert here — lose only gas (~$0.05-0.50)
}
}
Aave V3 Pool (mainnet): 0x87870Bca3F3fD6335C3F4ce8392D69350B4fA4E2
Flash loan fee: 0.05% (5 basis points). Free if you repay to an Aave debt position.
Dominant DEX: Aero (formerly Aerodrome, ~$500-600M TVL) — NOT Uniswap. In November 2025, Dromos Labs merged Aerodrome (Base) and Velodrome (Optimism) into a unified cross-chain DEX called Aero. Same contracts, same ve(3,3) model, new brand.
// Aerodrome Router: 0xcF77a3Ba9A5CA399B7c97c74d54e5b1Beb874E43 (Base)
struct Route {
address from;
address to;
bool stable; // true = stable pair (like Curve), false = volatile (like Uni V2)
address factory; // 0x420DD381b31aEf6683db6B902084cB0FFECe40Da
}
// Swap via Router
function swapExactTokensForTokens(
uint256 amountIn,
uint256 amountOutMin,
Route[] calldata routes,
address to,
uint256 deadline
) external returns (uint256[] memory amounts);
Pendle splits yield-bearing assets into principal and yield components:
SY_value = PT_value + YT_valueUse cases:
See addresses/SKILL.md for all verified protocol addresses (GMX, Pendle, Camelot, Aerodrome, Velodrome, SyncSwap, Morpho).